Insect transmission, host range, and field spread of potato calico

Abstract does not appear. First page follows.

Introduction

During investigations of the infectious nature of potato calico⁽⁶⁾ because of the increased prevalence of this disease in the field in 1929 and 1930, studies were made of the insect vectors, host range, and rate of spread in potato fields. Though still present in all the important potato districts of California, the disease has recently caused very slight loss. Maximum infection during 1932, 1933, and 1934 was less than 3 per cent, with less than 1 per cent average for the state.

In the search for other host plants, attention has been directed chiefly to cultivated species closely related to Solanum tuberosun, L., and several varieties of this species have also been tested for relative susceptibility. Insect transmission trials have been limited to the aphid Macrosiphum solanifolii Ashm.3 The rate of natural field spread was measured at Davis, Stockton, and Santa Clara.

The infectious nature of this disease has recently been questioned,⁽⁵⁾ although McKay and Dykstra⁽⁴⁾ state that their transmission trials in 1927 and again in 1929 were successful, antedating by three years the successful inoculations⁽⁶⁾ made by the present author.

The studies herein reported add further proof of the infectious nature of potato calico; they show that the virus is transmitted by a common insect, that both cultivated and wild plants are susceptible, and that the disease is readily spread in the field. Unless otherwise stated, these studies were conducted with the White Rose (Wisconsin Pride) variety, although previous investigations⁽⁷⁾ have demonstrated the susceptibility of certain other varieties.